[Plugin: NextGEN Gallery] Gallery layout probleem (fotos very close together, nearly on top of one a

Hi I am having trouble with the layout of my gallery. The thumbnail pictures are all very, very close together, nearly on top of one another, in stead of standing out one by one next to each other.

Can someone please help me get this straight?!

Thanks in advance, Sandra

http://wordpress.org/extend/plugins/nextgen-gallery/